A liquid crystal display device displays an image processed by the information-processing device, so that a user can perceive the image.
The liquid crystal display device, one of display devices, uses a liquid crystal, of which transmissivity is modulated according to electric fields so as to display an image.
The liquid crystal modulates the light transmissivity only. Therefore, the liquid crystal display device needs light passing through the liquid crystal so as to display an image.
A lamp generates the light. A Cold Cathode Fluorescent Lamp (CCFL) may be used as the lamp of the liquid crystal display device.
The cold cathode fluorescent lamp has many merits. For example, the cold cathode fluorescent lamp may be formed in a cylindrical shape having a very small diameter. The cold cathode fluorescent lamp generates white light that is similar to sunlight. The cold cathode fluorescent lamp has a long life span and generates a little amount of heat in comparison with incandescent lamp.
The cold cathode fluorescent lamp may be arranged variously according to a size of a liquid crystal display panel.
In a small sized or a middle sized liquid crystal display device, one or two cold cathode fluorescent lamps are sufficient to get enough luminance for displaying an image. In the small sized or the middle sized liquid crystal display device, a volume and a weight are important. The cold cathode fluorescent lamp is attached to a side of an optical distribution-regulating device called as a light-guide plate (LGP).
This liquid crystal display device is referred to as an edge-illumination type liquid crystal display device.
Comparatively, in a large sized liquid crystal display device, one or two cold cathode fluorescent lamps is not enough to generate sufficient luminance, because the area of effective display region is large.
Therefore, more than three cold cathode fluorescent lamps are needed to get sufficient luminance for displaying an image. In this case, the cold cathode fluorescent lamps are arranged in parallel with each other under the liquid crystal display panel for applying light to the liquid crystal display panel.
This liquid crystal display device is referred to as a direct-illumination type liquid crystal display device.
The direct-illumination type liquid crystal display device may have sufficient luminance to display an image. However, the direct-type liquid crystal display device has a variation of the luminance according to a region of the liquid crystal display panel.
A region of the liquid crystal display panel, disposed over the lamp, has a high luminance. A region of the liquid crystal display panel, disposed over a region between the lamps, has a low luminance.
Therefore, a diffusion plate is interposed between the liquid crystal display panel and the lamp so as to reduce the variation of the luminance.
In general, the diffusion plate comprises acryl resin. The diffusion plate comprising the acryl resin is light and may be easily manufactured.
However, when a display time becomes longer, specific characters of the diffusion plate comprising acryl resin becomes bad, so that display quality may be deteriorated.
Firstly, the diffusion plate comprising acryl resin gets curved or sags easily due to the heat generated by the lamp.
Secondly, the diffusion plate comprising acryl resin discolored easily due to the heat generated by the lamp. When the diffusion plate is discolored, the white light generated by the cold cathode fluorescent lamp is filtered into a different color, so that display quality becomes bad.